Chemical activation of in vitro matured dromedary camel (Camelus dromedarius) oocytes: optimization of protocols

Chemical activation of mammalian oocytes and its application in camelid reproductive biotechnologies: A review

Mammalian oocyte activation is a critical process occurring post-gamete fusion, marked by a sequence of cellular events initiated by an upsurge in intracellular Ca2+. This surge in calcium orchestrates the activation/deactivation of specific kinases, leading to the subsequent inactivation of MPF and MAPK activities, alongside PKC activation. Despite various attempts to induce artificial activation using distinct chemical compounds as Ca2+ inducers and/or Ca2+-independent agents, the outcomes have proven suboptimal. Notably, incomplete suppression of MPF and MAPK activities persists, necessitating a combination of different agents for enhanced efficiency. Moreover, the inherent specificity of activation methods for each species precludes straightforward extrapolation between them. Consequently, optimization of protocols for each species and for each technique, such as PA, ICSI, and SCNT, is required. Despite recent strides in camelid biotechnologies, the field has seen little advancement in chemical activation methods. Only a limited number of chemical agents have been explored, and the effects of many remain unknown. In ICSI, despite obtaining blastocysts with different chemical compounds that induce Ca2+ and calcium-independent increases, viable offspring have not been obtained. However, SCNT has exhibited varying outcomes, successfully yielding viable offspring with a reduced number of chemical activators. This article comprehensively reviews the current understanding of the physiological activation of oocytes and the molecular mechanisms underlying chemical activation in mammals. The aim is to transfer and apply this knowledge to camelid reproductive biotechnologies, with emphasis on chemical activation in PA, ICSI, and SCNT.

Recent advances in critical nodes of embryo engineering technology

The normal development and maturation of oocytes and sperm, the formation of fertilized ova, the implantation of early embryos, and the growth and development of foetuses are the biological basis of mammalian reproduction. Therefore, research on oocytes has always occupied a very important position in the life sciences and reproductive medicine fields. Various embryo engineering technologies for oocytes, early embryo formation and subsequent developmental stages and different target sites, such as gene editing, intracytoplasmic sperm injection (ICSI), preimplantation genetic diagnosis (PGD), and somatic cell nuclear transfer (SCNT) technologies, have all been established and widely used in industrialization. However, as research continues to deepen and target species become more advanced, embryo engineering technology has also been developing in a more complex and sophisticated direction. At the same time, the success rate also shows a declining trend, resulting in an extension of the research and development cycle and rising costs. By studying the existing embryo engineering technology process, we discovered three critical nodes that have the greatest impact on the development of oocytes and early embryos, namely, oocyte micromanipulation, oocyte electrical activation/reconstructed embryo electrofusion, and the in vitro culture of early embryos. This article mainly demonstrates the efforts made by researchers in the relevant technologies of these three critical nodes from an engineering perspective, analyses the shortcomings of the current technology, and proposes a plan and prospects for the development of embryo engineering technology in the future.

Development of in-vitro maturation protocol for rat oocytes; under simple culture vs co-culture with cumulus cell monolayer and its developmental potential via Parthenogenetic/artificial activation

BACKGROUND

Murine is the most abundantly used as laboratory animal models. There has been a tremendous amount of research including; their evolution, growth, physiology, disease modeling as well as genomic mapping. Rats and mice are the most widely used among them. Although both rats and mice fall under the same category still both are different a lot too. As regarding in vitro maturation and development mouse studies are well established as compared to rats which still lies in the early phase of development. So, we tried to figure out rat oocytes in vitro maturation and their developmental potential by performing 3 experiments i.e. superovulation, in vitro Maturation as simple culture (COC's only), and COC's & cumulus cells co-culture, which later further developed using parthenogenetic activation after IVM. Female Sprague Dawley rat 3-4 week used for these studies, we hyper-stimulated their ovaries using PMSG and hCG 150 IU/kg each. After that, we collected ovaries via dissection and retrieved oocytes. We matured them in TCM 199 supplemented with FSH, Estrogen, EGF, and Pyruvate. After maturation, we activated them using two types of activators i.e. Ethanol 7%, Ionomycin. After that, we saw and compared their developmental potential in vitro.

RESULTS

Oocytes matured in COC's and Cumulus cell monolayer co-culture (59% ± 4*) showed significantly more even growth and extrusion of the first polar body as compared to the COC's only culture (53.8 ± 7%*). While oocytes activated using Ionomycin showed more promising development until 8 cells/blastocyst level compared to ethanol 7%.

CONCLUSION

we concluded that COC's and cumulus monolayer co-culture is better than COC's only culture. Cumulus monolayer provides extra aid in the absorption of nutrients and supplements thus providing a better environment for oocytes growth. Also, we concluded that matured oocytes showed more developmental capacity after activation via ionomycin compared to ethanol.

In vitro embryo production (IVEP) in camelids: Present status and future perspectives

Camels are a fundamental livestock resource with a significant role in the agricultural economy of dry regions of Asia and Africa. Similarly, llamas and alpacas are an indigenous resource considered as beasts of burden in South America because of their surefootedness and ability to adapt. Camel racing, a highly lucrative and well-organized sport, camel beauty contests, and high demand for camel milk lead to a steady interest in the multiplication of elite animals by in vitro embryo production (IVEP) in this species during the last few decades. Although offspring have been produced from in vitro produced embryos, the technique is still not that well developed compared with other domestic animal species such as cattle. IVEP involves many steps, including the collection of oocytes from either slaughterhouse ovaries or live animals through ultrasound-guided transvaginal aspiration; in vitro maturation of these collected oocytes; collection and preparation of semen for fertilization; culture and passaging of cells for nuclear transfer, chemical activation of the reconstructed embryos, and in vitro culture of embryos up to the blastocyst stage for transfer into synchronized recipients to carry them to term. This review discusses the present status of all these steps involved in the IVEP of camelids and their future perspectives.

Development of prepubertal goat oocytes after their in vitro maturation and chemical activation

Experiments were conducted to study in vitro maturation of prepubertal goat oocytes and their developmental potential after chemical activation. In Experiment 1, cumulus-oocytes complexes collected from the ovaries of prepubertal goats slaughtered at a local abattoir were matured in vitro in TCM-199-based medium supplemented with 10 µg/ml luteinizing hormone (LH) (treatment 1) or 10 µg/ml LH + 0.1 mM l-cysteine (treatment 2). In Experiment 2, mature oocytes were activated with either 5 µM ionomycin or 7% ethanol. After 18 h, some oocytes were randomly fixed and stained to evaluate their chromatin status, while others were cultured in embryo culture medium to study their further development. In Experiment 3, oocytes activated with 5 µM ionomycin were cultured for 7 days in one of the four different culture media [Charles Rosenkrans medium (CR-1), TCM-199, potassium simplex optimization medium (KSOM) and synthetic oviductal fluid (SOF)] to study their developmental potential. The maturation rate in control, treatment 1, and treatment 2 media did not differ from each other (P > 0.05). However, the lowest degeneration of oocytes was observed in treatment 3 (P < 0.05) when compared with the other two groups. The proportion of activated oocytes was higher, while non-activated oocytes were lower in ionomycin group when compared with the group activated with ethanol (P < 0.05). The proportions of oocytes cleaved were 65.7, 56.8, 61.0 and 54.4% in CR-1, TCM-199, KSOM and SOF medium, respectively, with no significant difference. However, further development of cleaved oocytes was better in KSOM followed by SOF.

Effect of roscovitine pretreatment on in vitro maturation of oocytes and their subsequent developmental after chemical activation in dromedary camel (Camelus dromedarius)

Studies were conducted to evaluate an optimal concentration of roscovitine needed to maintain abattoir origin oocytes at germinal vesicle stage in experiment 1 and their subsequent maturation and developmental competence after chemical activation in experiments 2 and 3, respectively. The cumulus-oocyte complexes (COCs) aspirated from ovaries collected from a local slaughterhouse were cultured in TCM-199 based pre-maturation medium supplemented with 25, 50 or 75 μM roscovitine, depending on the experimental group. After 24 h, the COCs were denuded of cumulus, fixed and stained with aceto-orcein and examined for their nuclear status. They were classified as germinal vesicle, diakinesis, metaphase-I, metaphase-II and those with degenerated, fragmented, scattered, activated or without visible chromatin as others. In experiment 2, the COCs pre-matured in media supplemented with 50 μM roscovitine for 24 h were washed and kept for in vitro maturation along with another group of freshly collected COCs for 30 h. All the oocytes were fixed and stained to evaluate their nuclear status as described above. In experiment 3, all mature oocytes obtained from the COCs pre-matured in media supplemented with 50 μM roscovitine and those obtained from freshly collected group were activated by 5 mM ionomycin. Activated oocytes were cultured in embryo culture medium for a period of 7 days to evaluate their developmental potential. The proportion of oocytes at GV stage in the group pre-matured in media with 50 μM-was significantly (P < 0.01) higher when compared with the group having 25 μM of roscovitine. No difference was found in the proportion of GV stage oocytes in this group when compared with the freshly collected COCs. None of the oocytes reached to M-II stage in any of the three treatment groups. In experiment 2, no difference was observed in the proportion of oocytes reaching M-II stage between the groups after 30 h of in vitro culture; however, higher proportion of oocytes (P < 0.05) were classified as others in the pre-maturation group when compared with the group having freshly collected oocytes. In experiment 3, no difference was observed in the proportion of oocytes cleaving and those developing to the blastocyst stage between the pre-matured and freshly matured groups. In conclusion, the present study, for the first time, demonstrates the possible use of roscovitine as a meiotic inhibitor for camel oocytes. Keeping in view the ability of these oocytes to mature and develop to the blastocyst stage at par with the fresh oocytes, more flexible schedules for maturation and manipulation of such oocytes could be developed.

Optimization of parthenogenetic activation of rabbit oocytes and development of rabbit embryo by somatic cell nuclear transfer

The present study explored a suitable parthenogenetic activation (PA) procedure for rabbit oocytes and investigated the developmental potential of somatic cell nuclear transfer (SCNT) embryos using rabbit foetal fibroblasts (RFFs). The electrical activation had the optimal rate of blastocyst (14.06%) when oocytes were activated by three direct current (DC) pulses (40 V/mm, 20 μs each) followed by 6-dimethylaminopurine (6-DMAP) and cycloheximide (CHX) treatment; the blastocyst rate of ionomycin (ION) + 6-DMAP + CHX (12.07%) activation was higher than that of ION + 6-DMAP (8.6%) activation or ION + CHX (1.24%) activation; there was no significant difference in blastocyst rate between ION + 6-DMAP + CHX and DC + 6-DMAP + CHX groups. The blastocyst rate of ION + 6-DMAP + CHX-activated oocytes in the basic rabbit culture medium (M-199) + 10% foetal bovine serum (FBS; 14.28%) was higher than that in buffalo conditioned medium (5.75%) or G1/G2 medium (0), and the blastocyst rate was increased when M-199 + 10% FBS was supplemented with amino acids. Refreshing culture medium every day or every other day significantly increased the blastocyst rate. Treatment of donor cells with 0.5% FBS for 3-5 days increased blastocyst rate of SCNT embryos (33.33%) than no serum starvation (22.47%) or 0.5% FBS treatment for 6-9 days (23.61%); the blastocyst rate of SCNT embryos derived from nontransgenic RFFs was higher than that derived from transgenic RFFs by electroporation. The blastocyst development ability of SCNT embryos derived from RFFs by electroporation (32.22%) was higher than that of liposome (19.11%) or calcium phosphate (20.00%) transfection, and only the embryos from electroporation group have the EGFP expression (24.44%). In conclusion, this study for the first time systematically optimized the conditions for yield of rabbit embryo by SCNT.

Cytoplast source influences development of somatic cell nuclear transfer (SCNT) embryos in vitro but not their development to term after transfer to synchronized recipients in dromedary camels (Camelus dromedarius)

Studies were conducted to evaluate the adequate time for exposure of donor nucleus to oocyte cytoplast before its activation and the effect of oocyte source on the development of SCNT embryos in camels. A higher number of embryos cleaved and developed to blastocyst stage (P < 0.05) when couplets were activated between 1 and 2 h-than that of those activated at 0.5 h or more than 2 h post-fusion. A reduced number of reconstructed embryos cleaved (55.2 ± 7.6%) and developed to the blastocyst stage (20.5 ± 5.5%) when in vitro matured oocytes collected from the slaughterhouse were used as donor cytoplasts, compared to in vitro (71.3 ± 1.3 and 36.7 ± 7.3%) or in vivo matured (91.7 ± 8.3 and 35.4 ± 6.0%) oocytes obtained from live animals (P < 0.05), respectively. However, no differences were observed between the different types of oocyte sources on the establishment of pregnancies and delivery of offspring's. In conclusion, couplets activated 1-2 h post-fusion had higher in vitro developmental potential and oocytes collected from live animals were better in supporting the cleavage and blastocyst production in vitro than oocytes collected from slaughterhouse ovaries, however, all sources of oocytes can be utilized as donor cytoplasts and have the potential to support development of full-term calves after transfer into synchronized recipients.

Source, treatment and type of nuclear donor cells influences in vitro and in vivo development of embryos cloned by somatic cell nuclear transfer in camel (Camelus dromedarius)

Experiments were conducted to evaluate the effect of source, treatment and type of nuclear donor cells on embryonic and fetal development of somatic cell nuclear-transfer reconstructs in dromedary camel. In experiment 1, actively growing, serum starved or confluent skin fibroblast cells were used as nuclear donors. In experiment 2, skin fibroblasts from 4 different animals while in experiment 3, skin fibroblasts and cumulus cells from the same animal were used as nuclear donors. In all the three experiments, mature oocytes collected by transvaginal ovum pick up were used as recipient cytoplasts. All the blastocysts obtained were transferred to synchronized recipients on Day 5-6 after ovulation. In experiment 1, pregnancies were achieved from the embryos reconstructed with all the groups of cells, however, only 1 full term calf was delivered from the embryos reconstructed with serum-starved cells. In experiment 2, significant differences were observed in embryo development and establishment of pregnancies among the donor cell lines from different animals. Five cloned calves were delivered from the embryos reconstructed with skin fibroblast cells of 3 animals, while the sole pregnancy from fourth animal aborted on Day 224 of gestation. Three full term calves were delivered from pregnancies achieved by the embryos reconstructed with cumulus cells in experiment 3, while a single pregnancy achieved from skin fibroblast cells was lost on Day 296 of gestation. In conclusion, we observed that cell donor, cell type and their treatment affect the outcome of cloning by somatic cell nuclear transfer in camels.

First cloned Bactrian camel (Camelus bactrianus) calf produced by interspecies somatic cell nuclear transfer: A step towards preserving the critically endangered wild Bactrian camels

Studies were conducted to explore the possibility of employing dromedary camel (Camelus dromedarius) oocytes as recipient cytoplasts for the development of interspecies somatic cell nuclear transfer (iSCNT) embryos using skin fibroblast cells of an adult Bactrian camel (Camelus bactrianus) and Llama (Llama glama) as donor nuclei. Also, the embryos reconstructed with Bactrian cells were transferred into the uterus of synchronized dromedary camel recipients to explore the possibility of using them as surrogate mothers. Serum-starved skin fibroblast cells were injected into the perivitelline space of enucleated mature oocytes, collected from super-stimulated dromedary camels, and fused using an Eppendorf electroporator. After activation with 5μM ionomycin and 6-dimethylaminopurine, they were cultured at 38.5°C in an atmosphere of 5% CO₂, 5% O₂, and 90% N₂ in air. In experiment 1, Day 7 blastocysts were stained with Hoechst to count their cell numbers, while in experiment 2, they were transferred to synchronized dromedary recipients. A lower number (P < 0.05) of blastocysts were obtained from reconstructs utilizing fibroblast cells from Llama when compared with those reconstructed with dromedary and Bactrian fibroblast cells. However, no difference was observed in their cell numbers. In experiment 2, a higher (P < 0.05) proportion of blastocysts were obtained from the cleaved embryos reconstructed with Bactrian fibroblast cells when compared to those reconstructed with dromedary cells. Twenty-six Day 7 blastocysts reconstructed with Bactrian cells were transferred to 23 synchronized dromedary recipients with 5 pregnancies established on Day 30, however, only one of the pregnancies developed to term and a healthy calf weighing 33 kgs was born after completing 392 days of gestation. Unfortunately, the calf died on day 7 due to acute septicemia. In conclusion, the present study reports, for the first time, birth of a cloned Bactrian calf by iSCNT using dromedary camel as a source for oocytes as well as a surrogate for carrying the pregnancy to term.

Comparison of chemical, electrical, and combined activation methods for in vitro matured porcine oocytes

Factors influencing porcine oocyte activation were systematically studied. This study included (1) the effect of ionomycin plus various chemical agents on activation, (2) comparison of different electrical activation parameters, (3) optimization of combined activation, and (4) evaluation of the optimized protocols. The results showed that (1) blastocyst rates of ionomycin (Ion) + 6-dimethylaminopurine (6-DMAP) (29.7 ± 1.1%), Ion + cytochalasin B (CB) + cycloheximide (CHX) (29.8 ± 1.2%), Ion + CB + 6-DMAP (30.4 ± 1.6%), and Ion + CB + CHX + 6-DMAP (30.2 ± 2.7%) were significantly higher than Ion + CHX (15.8 ± 1.5%, p < 0.05); (2) the parthenogenetic blastocyst formation of electrical activation was optimal when oocytes were activated by three direct current (DC) pulses of 1.00 kV cm(-1) for 80 μs (39.5 ± 1.1%); (3) blastocyst rates of DC + CB + CHX (55.4 ± 1.2%) and DC + CB + 6-DMAP (50.4 ± 2.9%) were significantly higher than DC + 6-DMAP, DC + CB + CHX + 6-DMAP, electrical activation, and chemical activation alone (p < 0.05); and (4) approximately 84% of parthenogenetic blastocysts yielded by the optimized protocol were diploid, which was significantly higher than that of electrical activation blastocysts (40%). Using the optimized electrical and combined activation protocol, high blastocyst rates were generated by intracytoplasmic sperm injection (ICSI) (34.6 ± 1.1%), cytoplasmic microinjection (CI) (52.3 ± 2.2%), and handmade cloning (HMC) (31.2 ± 1.0%), respectively. This study concludes that the optimal activation protocol of in vitro matured porcine oocytes was combined activation with parameter as three DC pulses of 1.00 kV cm(-1) for 80 μs plus CB and CHX treatment.

Roscovitine in combination with calcium ionophore induces oocyte activation through reduction of M-phase promoting factor activity in mice

The aim of the present study was to determine oocyte activation and change in M-phase promoting factor (MPF) activity induced by treatment with calcium ionophore and roscovitine in comparison with those induced by treatment with roscovitine alone and treatment with calcium ionophore and puromycin in mice. Freshly ovulated oocytes obtained from 6–8-week-old mice were divided into five groups (no activation treatment; 5 μM calcium ionophore A23187; 50 μM roscovitine; 5 μM calcium ionophore and 10 μg/ml puromycin; and 5 μM calcium ionophore and 50 μM roscovitine) and were incubated for 6 h. Oocyte activation, assessed by morphological changes, and changes in MPF activity in the five groups at 0, 2, 4 and 6 h of incubation were examined. Activated oocytes were defined as oocytes with at least one pronucleus. Oocytes treated with roscovitine alone were not activated during the 6-h incubation period. All of the oocytes in the calcium ionophore with puromycin group and in the calcium ionophore with roscovitine group were activated. The percentage activity of MPF in oocytes treated with roscovitine alone was decreased after 2 h and increased after 4 h of incubation. The percentage activity of MPF in oocytes treated with calcium ionophore and roscovitine was significantly decreased with suppression of MPF activity being maintained for 6 h, and this change was similar to that in oocytes treated with calcium ionophore and puromycin. Roscovitine with calcium ionophore is effective for induction of oocyte activation through suppression of MPF activity in mice.

Role of AMPK throughout meiotic maturation in the mouse oocyte: evidence for promotion of polar body formation and suppression of premature activation

This study was conducted to assess the role of AMPK in regulating meiosis in mouse oocytes from the germinal vesicle stage to metaphase II. Exposure of mouse cumulus cell-enclosed oocytes (CEO) and denuded oocytes (DO) during spontaneous maturation in vitro to AMPK-activating agents resulted in augmentation of the rate and frequency of polar body formation. Inhibitors of AMPK had an opposite, inhibitory effect. In addition, the AMPK inhibitor, compound C (Cmpd C) increased the frequency of oocyte activation. The stimulatory action of the AMPK-activating agent, AICAR, and the inhibitory action of Cmpd C were diminished if exposure was delayed, indicating an early action of AMPK on polar body formation. The frequency of spontaneous and Cmpd C-induced activation in CEO was reduced as the period of hormonal priming was increased, and AMPK stimulation eliminated the activation response. Immunostaining of oocytes with antibody to active AMPK revealed an association of active kinase with chromatin, spindle poles, and midbody during maturation. Immunolocalization of the α1 catalytic subunit of AMPK showed an association with condensed chromatin and the meiotic spindle but not in the spindle poles or midbody; α2 stained only diffusely throughout the oocyte. These data suggest that AMPK is involved in a regulatory capacity throughout maturation and helps promote the completion of meiosis while suppressing premature activation.